Apparatus for electrolytic production of a metal product from fused salts



Dec. 2, 1958 K. F. GRIFFITH 2,862,863

APPARATUS FOR ELECTROLYTIC PRODUCTION OF A METAL PRODUCT FROM FUSED SALTS Filed Sept. 25, 1957 IN VEN TOR.

Kenneth F. Griffith United States Patent APPARATUS FOR ELECTROLYTIC PRODUCTION OF A METAL PRODUCT FROM 'FUSED SALTS Kenneth F. Grifiith,jNewark, N. J.

Application September 23, 1957, Serial No. 685,754

3 Claims. (Cl. 204-227) My invention relates to the electrolytic productioncf metals such as sodium, potassium, lithium, cesium, rubidium andmagnesium including their alloys, from an electrolyte such as the respective halideor halides which has a greater density than the metal or alloys.

In the electrolysis of an electrolyte into a metal product and a halogen product, itis easier to operate an electrolytic cell when the metal product can be collected in the bottom of the cell rather than at the topof the cell where the halogen gas collects. When the metal product is less dense than the electrolyte, the advantage of collecting the metal product at the bottom of thecell has been achieved by collecting themetal product in a liquid metal cathode of greater density than the electrolyte. However, the use of a heavy liquid ,metal cathode such as molten lead necessitates subsequent separation of the collected metal product from the heavy-liquid metal constituting the cathode.

The object of my present invention is to collect a metal product which is less dense than the electrolyte without the use of a heavy liquid metalcathode.

I achieve this object by usinga porous cathode which is saturated with liquid metal product for the purpose of soaking up the metal product. as fast as it isformed on the cathode surface. Excess liquid metal product collecting in the porous cathode is sucked out therefrom into a collector for said liquid metal product. The suction applied to draw the liquid metal product out of the porous cathode has to be so strong that the metal product is prevented from bubbling .upward from the upper surface of the porous cathode, but not as strong as to suck electrolyte through the porous cathode.

The porous cathode is located under the anode so that as little aspossible of the gaseous halogen being formed at the anode will contact it. The surface portion of the porous cathode from which metal product is being sucked maybe anyarea on which metal; product is not being formed.

The porous material comprising the porous cathode must be resistant to attack from both the metal product and the electrolyte at the operating temperature of the cell, and also must be able to be wetted thoroughly by the liquid metal product while being immersed in the electrolyte at the operating temperature of thecell. The porous cathode is comprised usually of sintered. particles of a refractory metal such as iron, stainless steel, or molybdenum; however, other forms and other materials may be used.

The anode may be in any shape and position which allows the by-product gas forming on it to escape upward easily.

Suitable metal products to be formed and collected on the porous cathode are: sodium, potassium lithium, cesium, rubidium and magnesium, or alloys .of two' or more such metal products. For example from a suitable electrolyte an alloy of sodium and potassium ,may be produced and collected on the porous cathode.

Any of the fused electrolyte compositions used in Patented Dec."'2, s

electrolytic cells for producing the. aforesaid metal products may be used in my new process providing the. metal product is. the only cathode product.

LI. prefer that the size of the pores in the porous cathode be as uniformas possible. I also prefer to operate the cell at such lowest. temperature {that will allow both the electrolyte and the metal product to be in liquid phase. .I also prefer to have all portions of the p'orous cathode which contact. the electrolyte to been .the same'level.

I'further prefer that the anode be -in theform of .a

ence numbersindicate the same or equivalentelements. 20

Inthe drawing, Fig. 1 shows an electrolytic cell 11 which contains asuitable molten halide electrolyte 12 such as a eutectic mixture of two or morealkali metal chlorides maintained in molten condition by not shown electric heaters or:other suitable means arranged within the cell. The ,anode 13 held by supportlfi .and'the cathode .14 are each connected to. asuitable source of direct currentwby means of electric leads16. {The anode "13 which maybe made of graphite .or a metal such as nickel hasadvantageously the form of a grid or screen of such 'designthatfthe halogen gas mayescapexupward .mostea ly and the total surface area of the anode grid "13.von,which thehalogengas is formed is preferably considerably larger than the area .of the cathode 14 on which ,the metal product is formed because assubstantial portion .ofgthe area of the anode iscovered by and electrically insulated from the electrolyte by the halogen gas forming on it. The porous cathode'14. may be fabricated from a suitable sintered refractory metal such as sintered stainless steel and is tightlyplaced in a .box o'r;similar member 17whichforms a suctionchamber to prevent any electrolyte from'leaking thereinto. The box 17"and its outlet conduit18 are. filled with liquid metaLproduct prior to, the starting of the operation and thisjliquid metal product is held-therein .by suitable .closure means .not shown in the drawing 'When.the;cell is operating,

liquid metal product is formed onthe uppersurface'of the porous cathode 1'4, passes through the porous cathode into cathode box17, and is withdrawn therefromthrough conduit18 by creating a pressure differential across the porous cathode such pressure differential being maim tained within"desirablelimits by the application of a controlled suction on the metal product iflowingout of conduitltl, such suction being, effected:by;aconventional apparatusitnot shown) outside-the-cell.

The halogengaslfliformed on the anode 13j-bubbles up through the molten ;electrotype 12, collects i'n the upper portion of the-cell-ll and is vented from the-cell through a snitableiconduitztl. Since,jin'all-cases except when .a highly puritiedelectrotype is used; some sediment tends to collect' on the 'upper;surface of the-cathode 14, a wiper 21 may be providedto brush all sediment off-"the top of th e anodeinto. the lower portion ;ofthecell. This wiper is usually made out of'a 'non conductivematerial .such'as -glass'vicor, quartz or the like andgmaybe -mechanically or;manual ly actuated even whileithe cell is operating -by a push pull motionimparted to rodfil QThe gland where rod 22 passes, through the wall ofthe cell 11 is sealed by a metal bellows23 or any other type or suitable gland seal. If desirable, means may be provided to raise or" lower the anode13-relative to .the cathode 14 to facilitate the cleaning of the cathode surface and to permit to selectively distance the same from each other.

The modified embodiment illustrated in Fig. 2 comprises like the embodiment shown in Fig. l a cell 11, an anode 13 held by support 15, a cathode 14 and a wiper 21 actuated by the rod 22 which passes through the seal 23. The cathode box 17 is provided with or attached to a syphon 24 located within the cell 11 and submerged in the electrotype 12. This syphon 24 effects an automatic controlled suction on the liquid metal product in the box 17, the suction force being proportional to the difference in level between the top surface of the porous cathode 14 and the level at which the liquid metal product escapes from syphon 24. The thus escaping liquid metal product bubbles upward through the electrolyte 12 and enters a collector 25 wherein it accumulates above the depressed level of the electrolyte to leave the collector 25 through the overflow conduit 26.

Example I In a cell of the type shown in Fig. 1 or Fig. 2 an electrolyte comprised of 60 atomic percent of potassium chloride and 40 atomic percent of lithium chloride is melted and maintained at about 375 C. The cell is a square stainless steel box 30 cm. by 30 cm. and 30 cm. deep. The porous anode is square and has an area of about 12 by 12 cm. Its upper surface lies on a plane cm. above the bottom of the cell, and it is comprised of 5 micron sintered stainless steel having a thickness of approximately 0.5 cm. The electrolyte covers the cathode to depth of cm. The anode is formed by a grid of graphite perforated with inch holes, having 60% open area and a thickness of about 1 inch. The anode is suspended on each corner by a graphite rod, and has its lower surface of the cathode. No diaphragm is used, between the anode and the cathode. Before the opera tion of the cell is started, the molten electrolyte which fills the pores of the cathode, the cathode box 17 and either the outlet pipe 18 (Fig. 1) or the syphon 24 (Fig. 2) respectively, is displaced with molten sodium. The molten sodium saturates the porous cathode 14. A 6-volt electric battery may be used to power the cell with about 6 volts at approximately 100 amperes. During the first part of each run the upper surface of the porous cathode tends to acquire a light deposit of impurities from the electrolyte which are easily brushed ofi. However, the further the run progresses the less is the tendency for impurities to settle on the cathode. The strong current of electrolyte flowing across the upper surface of the cathode is powered by the rising stream of chloride which is a great aid in keeping the upper portion of the cathode clean and allowing the sludge to settle at the bottom of the cell where the electrolyte currents are much weaker. As the run progresses the sodium in the cathode and the cathode box is replaced with molten potassium and lithium. At an average current of 100 amperes, about 110 grams of chlorine is produced in one hour. When 6 volts is used to power the cell, the amperage may be adjusted and held constant by raising or lowering the anode. If desired the cell can be operated on considerable less than 6 volts by decreasing the distance between the anode and the cathode and using lower amperage. Very high current efliciency is obtained if the anode is not brought so close to the cathode that chlorine washes the metal product forming on the cathode. However, the voltage required to operate the cell at a given amperage becomes less as the anode and cathode are brought closer together. The molten metal product being an alloy of potassium and lithium which assembles in the cathode box 17 is recovered therefrom by suction as described above either through the outlet conduit 18 shown in Fig. 1 or through the syphon 24 and collector 25 shown in Fig. 2.

Example 2 Sodium with a relatively small percent of calcium may be recovered 'in the manner abovefrom an electrolyte 4 composed of about 59% CaCl and 41% NaCl at an operating temperature of 600 C.

Example 3 Sodium with a relatively small percent of cesium may be recovered in the manner described above from an electrolyte composed of a eutectic mixture of CeCl and and NaCl at an operating temperature of 500 C.

Example 4 Magnesium may be recovered in the manner described above from an electrolyte of MgCl having a possible addition of NaCl up to about 50% at a temperature of 675 C.

While specific embodiments of my invention have been shown and described in detail to illustrate the application of the principles of my invention, it will be well understood that the same may be otherwise embodied and performed without departing from such principles and without avoiding the scope of my appended claims.

What I claim as my invention is:

1. In an electrolytic cell for producing metal products which are less dense than the fused electrolyte the improvement comprising a substantially flat porous cathode adapted to be saturated with liquid metal product; an anode having the shape of a grid or screen permitting gaseous by-products formed on the anode to pass therethrough; said anode and said cathode extending in substantially horizontal planes immersed in the electrolyte, the anode being located over said cathode; a suction chamber tightly attached to the cathode in opposite relation to the anode, the cathode forming the top cover of said chamber; a suction piping attached to said suction chamber to suck liquid metal product deposited on and saturating the porous cathode into and from said chamber; means to create and to control the suction action; and receiving means collecting the sucked liquid metal product apart from the electrolyte and the gaseous halide products.

2. In an electrolytic cell for producing metal products which are less dense than the fused electrolyte the improvement comprising a substantially flat porous cathode adapted to be saturated with liquid metal product; an anode having the shape of a grid or screen permitting gaseous by-products formed on the anode to pass therethrough; said anode and said cathode extending in substantially horizontal planes immersed in the electrolyte, the anode being located over said cathode; a suction chamber tightly attached to the cathode in opposite relation to the anode, the cathode forming the top cover of said chamber; a syphon attached to said suction chamber to suck liquid metal product deposited. on and saturating the porous cathode into and from said chamber; said syphon leading from said chamber to a level in the cell higher than the level of the surface of the cathode on which liquid metal product is deposited; a collector collecting the liquid metal product bubbling upward from the syphon through the electrolyte within the cell; and a receptacle receiving the liquid metal product from said collector.

3. An electrolytic cell according to claim 1 comprising a scraper for cleaning the surface portion of the cathode upon which the metal product is deposited and means to actuate said scraper from outside the cell.

References Cited in the file of this patent UNITED STATES PATENTS 513,661 Vautin Jan. 30, 1894 679,253 Cowles July 23, 1901 690,365 Gintl Dec. 31, 1901 1,583,704 Sheppard et al. May 4, 1926 1,921,377 Ward Aug. 8, 1933 2,257,746 Janes et a1 Oct. 7, 1941 2,616,845 Kreml Nov. 4, 1 952. 

1. IN AN ELECTROLYTIC CELL FOR PRODUCING METAL PRODUCTS WHICH ARE LESS DENSE THAN THE FUSED ELECTROLYTE THE IMPROVEMENT COMPRISING A SUBSTANTIALLY FLAT POROUS CATHODE ADAPTED TO BE SATURATED WITH LIQUID METAL PRODUCT; AN ANODE HAVING THE SHAPE OF A GRID OR SCREEN PERMITTING GASEOUS BY-PRODUCTS FORMED ON THE ANODE TO PASS THERETHROUGH; SAID ANODE AND SAID CATHODE EXTENDING IN SUBSTANTIALLY HORIZONTAL PLANES IMMERSED IN THE ELECTROLYTE, THE ANODE BEING LOCATED OVER SAID CATHODE; A SUCTION CHAMBER TIGHTLY ATTACHED TO THE CATHODE IN OPPOSITE RELATION TO THE ANODE, THE CATHODE FORMING THE TOP COVER OF SAID CHAMBER; A SUCTION PIPING ATTACHED TO SAID SUCTION CHAMBER TO SUCK LIQUID METAL PRODUCT DEPOSITED ON AND SATURATING THE POROUS CATHODE INTO AND FROM SAID CHAMBER; MEANS TO CREATE AND TO CONTROL THE SUCTION ACTION; AND RECEIVING MEANS COLLECTING THE SUCKED LIQUID METAL PRODUCT APART FROM THE ELECTROLYTE AND THE GASEOUS HALIDE PRODUCTS. 